1. Field of the Invention
The present invention relates to a combination stopper and shield closure for body fluid collection tubes and, more particularly, relates to a closure for an evacuated body fluid collection tube having a headless stopper that minimizes needle penetration force by reducing radial compression interference in the stopper.
2. Background Description
An evacuated body fluid collection tube is commonly used by a doctor, phlebotomist or nurse to draw a sample of body fluid from a patient in a hospital or doctor's office for diagnostic testing. During the use of such a tube, a double-ended needle in a needle holder is inserted in a vein of the patient and the evacuated tube is inserted into the open end of the holder until the needle in the holder pierces the tube's closure. The vacuum in the tube then draws a body fluid sample from the patient into the tube. When draw is completed the tube is removed from the holder and replaced by additional tubes or the holder and tube are removed from the patient's vein. When the body fluid sample in the tube is to be tested, the test sample can either be removed from the tube by removing the closure from the open end of the tube or using a syringe to pierce the closure and draw the test sample from the tube. These alternative methods of removing the test sample from the tube, however, present divergent problems. If the closure is removed from the open end of the tube, it is important that the stopper remain attached to the shield. To avoid this problem it is common to increase the compression forces on the stopper to firmly hold the stopper in the shield. However, if a syringe is used to remove the test sample by piercing the closure it is imperative that the compression forces on the stopper be minimized, since compression of the stopper increases the force needed to pierce the stopper.
Moreover, when using either method it is important for the closure to fit securely on the open end of the tube and maintain the vacuum in the tube before, during and after the collection procedure. The vacuum in the tube must be sufficient to draw body fluid into the tube, since body fluid must be drawn as quickly as possible to minimize the amount of time a patient has one end of the needle in their body, which can be uncomfortable and cause pain. For example, if the vacuum in the tube is deficient, subsequent removal of the tube from the needle holder and insertion of another tube in the needle holder would be necessary which prolongs the unpleasant procedure.
Current closures for evacuated body fluid collection tubes include a plastic shield containing a rubber stopper having an enlarged head portion and a plug portion extending from the bottom of the head portion to be received within and seal the open end of the tube. The stopper in such closures is commonly held within the shield by compression forces on the head of the stopper. An example of this type of closure is described in U.S. Pat. No. 4,967,919 (Earhart).
Those skilled in the art should therefore appreciate the trade-off problems that exist when designing a closure for evacuated body fluid collection tubes between (1) the penetration force necessary for inserting a needle through the closure and (2) the forces needed to withdraw the closure frown the tube and retain the stopper within the shield. Using plastic shields over rubber stoppers provides a firm gripping surface to help the user remove the closure from the evacuated tube and overcome the force of the vacuum within the tube. However, the need for retaining the stopper within the shield during removal has resulted in increased radial compression on the stopper from the shield, which detrimentally increases needle penetration force.